Thermally initiated acid catalyzed reaction between silyl hydride and siloxane

ABSTRACT

A composition contains a mixture of silyl hydride, a siloxane, a Lewis acid catalyst and an amine having the following formula: R 1 R 2 R 3 N; where the nitrogen is not a member of an N═C—N linkage and where each of R 1 , R 2 , and R 3  is independently selected from a group consisting of hydrogen, alkyl, substituted alkyl, and conjugated moieties; and wherein at least one of R 1 , R 2  and R 3  is a conjugated moiety connected to the nitrogen by a conjugated carbon.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a composition comprising a silyl hydride, siloxane, Lewis acid catalyst and amine blocking agent for the Lewis acid catalyst. Heating the composition releases the Lewis acid catalyst from the amine blocking agent and allows it to trigger reaction between the silyl hydride and siloxane.

Introduction

Strong Lewis acids are known catalysts for numerous reactions. For instance, the Piers-Rubinsztajn (PR) reaction between silyl hydride and silyl ether is a well-known reaction catalyzed by a strong Lewis acid, particularly tris(pentafluorophenyl) borane (“BCF”). Similar Lewis acid catalyzed reactions include rearrangement reactions between silyl hydride and polysiloxane as well as silyl hydride and silanols. See, for instance Chem. Eur. J. 2018, 24, 8458-8469.

Lewis acid catalyzed reactions, such as the PR reaction, tend to be rapid reactions even at 23 degrees Celsius (° C.). The high reactivity of these reaction systems limits their applications. The reactions may be desirable in applications such as coatings and adhesives; however, the systems must be stored in a multiple-part system in order to preclude reaction prior to application. Even so, the reaction can occur so quickly once the components are combined that there is little time to apply the reactive system. It is desirably to identify a way to control the Lewis acid catalyzed reactions and, ideally, provide them as one-part systems comprising reactants and Lewis acid catalyst in a form that is stable at 23° C. but that can be triggered to react when desired.

Ultraviolet (UV) light sensitive blocking agents have been combined with Lewis acids in order to form blocked Lewis acids that release Lewis acid upon exposure to UV light. Upon exposure to UV light the blocking agent dissociates from the Lewis acid leaving the Lewis acid free to catalyze a reaction. A challenge with systems comprising these blocked Lewis acids is that they need to be kept in the dark in order to maintain stability. Moreover, they need to be exposed to UV light in order to initiate reaction—and for thick compositions it can be difficult to obtain UV light penetration to initiate cure quickly throughout the composition.

Notably, amines have been looked at in combination with Lewis acids in PR reaction type systems. However, amines are reported to completely suppress the reaction. See, for instance, Chem. Comm. 2010, 46, 4988-4990 at 4988. It was later identified that most amines complex essentially irreversibly with the Lewis acid catalysts, yet triaryl amines were found to be an exception and do not compromise Lewis acids in catalyzing PR reactions. See, Chem. Eur. J. 2018, 24, 8458-8469 at 8461 and 8463.

It is desirable to identify a way to prepare a one-part system for a Lewis-acid catalyzed reaction that is stable at 23° C. even when exposed to UV light, but that can be triggered to react when desired, preferably at a temperature below 100° C.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a solution to the problem of identifying a way to prepare a one-part system for a Lewis-acid catalyzed reaction that is stable at 23° C. even when exposed to UV light, but that can be triggered to react when desired. In particular, the present invention provides a solution to such a problem in a reaction between silyl hydride and siloxanes. Yet more, the present invention provides such a solution that is triggered to react when heated so as to have a desirable 90° C. Cure Speed, that is a 90° C. Cure Speed of 30 minutes or less, preferably 15 minutes or less, more preferably 10 minutes or less, even more preferably 5 minutes or less, yet even more preferably one minute or less and most preferably 30 seconds or less.

The present invention is a result of surprisingly and unexpectedly discovering specific amines that complex with a Lewis acid catalyst and block the activity of the Lewis acid catalyst at 23° C. but release the Lewis acid catalyst when heated. As a result, the specific amines are thermally triggerable blocking agents for the Lewis acid catalyst that block a Lewis acid catalyst at 23° C. yet release the Lewis acid catalyst to catalyze reactions at elevated temperatures such as 90° C. or higher, or 100° C. or higher. This is surprising in view of previous understanding in the art. As noted above, current understanding is that amines either irreversibly complex with Lewis acid catalysts or fail to compromise Lewis acid catalysts in Lewis acid catalyzed reactions. See, Chem. Comm. 2010, 46, 4988-4990 at 4988 and Chem. Eur. J. 2018, 24, 8458-8469 at 8461 and 8463.

The present discovery of amines that work as thermally triggered blocking agents for Lewis acid catalysts enables the present inventive composition which serve as one-component reaction systems comprising a Lewis acid catalyst, silyl hydride and siloxanes along with the amine blocking agent.

In a first aspect, the present invention is a composition comprising a mixture of silyl hydride, a siloxane, a Lewis acid catalyst and an amine having the following formula: R¹R²R³N; where the nitrogen is not a member of an N═C—N linkage and where each of R¹, R², and R³ is independently selected from a group consisting of hydrogen, alkyl, substituted alkyl, and conjugated moieties; and wherein at least one of R¹, R² and R³ is a conjugated moiety connected to the nitrogen by a conjugated carbon.

In a second aspect, the present invention is a process comprising the steps of: (a) providing a composition of the first aspect; and (b) heating the composition to a temperature sufficient to dissociate the Lewis acid catalyst from the amine.

Compositions of the present invention are suitable, for example, as one-component systems for coatings and adhesives.

DETAILED DESCRIPTION OF THE INVENTION

Test methods refer to the most recent test method as of the priority date of this document when a date is not indicated with the test method number. References to test methods contain both a reference to the testing society and the test method number. The following test method abbreviations and identifiers apply herein: ASTM refers to ASTM International; EN refers to European Norm; DIN refers to Deutsches Institut für Normung; and ISO refers to International Organization for Standardization.

“Multiple” means two or more. “And/or” means “and, or as an alternative”. All ranges include endpoints unless otherwise indicated. Products identified by their tradename refer to the compositions available from the suppliers under those tradenames at the priority date of this document unless otherwise stated herein.

The composition of the present invention comprises a mixture of silanol and/or silyl ether, silyl hydride, a Lewis acid and an amine. The composition is useful as a reactive mixture that is stable at 23° C. but can be heat-triggered to cure even at a temperature below 100° C.

“Siloxane” refers to a molecule that contains at least one siloxane (Si—O—Si) linkage. Desirably, the siloxane of the present invention is a “polysiloxane”, which refers to a molecule that contains multiple Si—O—Si linkages. Polysiloxanes comprise siloxane units that are typically referred to as M, D, T or Q units. Standard M units have the formula (CH₃)₃SiO_(1/2). Standard D units have the formula (CH₃)₂SiO_(2/2). Standard T units have the formula (CH₃)SiO_(3/2). Standard Q units have the formula SiO_(4/2). M-type, D-type and T-type units can have one or more methyl group replaced with hydrogen, or some other moiety.

“Silyl hydrides” are molecules that contain a silicon-hydrogen (Si—H) bond and can contain multiple Si—H bonds.

“Alkyl” is a hydrocarbon radical derived from an alkane by removal of a hydrogen atom. “Substituted alkyl” is an alkyl that has an atom, or chemical moiety, other than carbon and hydrogen in place of at least one carbon or hydrogen.

“Aryl” is a radical derived from an aromatic hydrocarbon by removal of a hydrogen atom. “Substituted aryl” is an aryl that has an atom, or chemical moiety, other than carbon and hydrogen in place of at least one carbon or hydrogen.

“Conjugated” refers to a set of alternating carbon-carbon single and double and/or triple bonds whose p-orbitals are connected allowing for delocalized electrons across the carbon bonds. “Conjugated carbon” refers to a carbon in the set of alternating carbon-carbon single and double bonds that are conjugated. “Non-conjugated” refers to a carbon that is not part of a conjugated system. “Aromatic” refers to a cyclic planar conjugated molecule.

“Blocking agent” is a component that binds to a second component in order to prevent activity of the second component in some way. For example, a blocking agent on a catalyst precludes the catalyst from catalytic activity while complexed with the blocking agent.

The Lewis acid catalyzed reaction between a siloxane and silyl hydride is a rearrangement reaction generally represented by the following reaction:

Si′—H+Si—O—Si+Lewis Acid→Si′—O—Si+Si—H+Lewis Acid

This rearrangement reaction is useful to form new siloxane bonds and to form crosslinked polysiloxane systems. A particularly desirable characteristic of this reaction over other Lewis acid catalyzed reactions such as Piers-Rubinsztajn (PR) reaction is that this reaction does not typically generate volatile side products that can create bubbles when the reaction is used to cure a siloxane polymer. Hence, the reaction is ideal for making clear cured compositions and films.

The present invention includes a composition comprising a mixture of silyl hydride, a siloxane, a Lewis acid catalyst and a particular amine. It has been discovered that the particular amines of the present invention act as blocking agents for the Lewis acid catalyst at 23° C., but release the Lewis acid catalyst at elevated temperatures (for example, 80° C. or higher or 90° C. or higher). As a result, the compositions of the present invention are stable at 23° C. but are thermally triggered to undergo Lewis acid catalyzed reaction at elevated temperatures. Such a composition achieves an objective of the present invention to provide a “stable” one-part reactive system for a Lewis acid catalyzed reaction that is “stable” at 23° C. “Stable” at 23° C. means that the reactive system does not gel at 23° C. in one hour or less, preferably in 3 hours or less, more preferably in 6 hours or less, even more preferably in 12 hours or less and even more preferably in 24 hours or less. Evaluate shelf stability using the “23° C. Stability Test” in the Examples section, below. The compositions of the present invention further provide a one-part reactive system for a Lewis acid catalyze reaction that, while stable at 23° C., is triggered when desired by heating. In particular, compositions of the present invention cure at 90° C. in 30 minutes or less, preferably in 10 minutes or less, more preferably in 5 minutes or less and even more preferably in one minute or less. Determine rate of curing at 90° C. using the “Cure Speed at 90° C.” test in the Example section, below.

Siloxane

Desirably, the siloxane component is a polysiloxane, containing multiple siloxane linkages. Polysiloxanes comprise multiple siloxy (SiO) groups. Siloxy containing groups are typically designated as M, D, T or Q groups. The polysiloxane can be linear and comprise only M (≡SiO_(1/2)) type and D (≡SiO_(2/2)) type units. Alternatively, the polysiloxane can be branched and contain T (-SiO_(3/2)) type and/or Q (SiO_(4/2)) type units. Typically, M, D, T and Q units have methyl groups attached to the silicon atoms where oxygen is not attached to provide a valence of four to each silicon atom and each oxygen is attached to the silicon of another unit. Referring to these as M, D, T and Q “type” units means that groups such as those selected from a group consisting of hydrogen, alkyl, substituted alkyl, aryl, and substituted aryl groups can be bound to the silicon atoms in place of one or more methyl. For instance, M^(H) is an M-type unit where one methyl of a typical M unit is replaced with a hydrogen.

The polysiloxane can have a degree of polymerization (DP) of 10 or more, preferably 20 or more, more preferably 30 or more, and can be 40 or more 50 or more, 75 or more, 100 or more, 250 or more, 500 or more, 1000 or more, 2,000 or more, 4,000 or more, 6,000 or more and even 8,000 or more while at the same time is typically 10,00 or less, preferably 8,000 or less, 6,000 or less, 4,000 or less, 2,000 or less, 1,000 or less, 800 or less, 600 or less, 400 or less, 200 or less or even 100 or less. DP corresponds to the number of siloxy groups there are in the molecule and can be determined by silicon-29 nuclear magnetic resonance (²⁹Si NMR) spectroscopy.

The siloxane component can contain a Si—H bond, which means it can also serve as a silyl hydride component. In fact, the siloxane component and the silyl hydride component can be the same molecule in the present invention. Alternatively, the siloxane component and the silyl hydride component can be different molecules. In fact, the siloxane molecule can be free of Si—H bonds and/or the silyl hydride component can be free of Si—O—Si linkages.

Examples of suitable siloxanes without Si—H bonds include XIAMETER™ PMX-200 Silicon Fluids available from The Dow Chemical Company.

Examples of suitable siloxanes that contain Si—H bonds include poly(methylhydrosiloxane and poly(dimethylsiloxane-co-methylhydrosiloxane), trimethylsilyl terminated, both of which are available from Sigma-Aldrich. Additional examples of suitable siloxanes that contain Si—H bonds include pentamethyldisiloxane, bis(trimethylsiloxy)methyl-silane, tetramethyldisiloxane, tetramethycyclotetrasiloxane, and hydride terminated poly(dimethylsiloxane) such as those available from Gelest under the tradenames: DMS-H03, DMS-H25, DMS-H31, and DMS-H41.

Typically, the concentration of siloxane in the composition is 70 weight-percent (wt %) or more, 75 wt % or more, 80 wt % or more, 85 wt % or more, even 90 wt % or more while at the same time is typically 90 wt % or less, 85 wt % or less, 80 wt % or less, or even 75 wt % or less based on combined weight of silyl hydride, siloxane, amine and Lewis acid catalyst in the composition.

Silyl Hydride

The silyl hydride contains one, preferably more than one, Si—H bond. The Si—H bond is typically part of polysilane (molecule containing multiple Si—H bonds) or polysiloxane. Silyl hydrides containing multiple Si—H bonds are desirable as crosslinkers in compositions of the present invention because they are capable of reacting with multiple siloxane linkages.

The silyl hydride of the present invention can be polymeric. The silyl hydride can be linear, branched or can contain a combination of linear and branched silyl hydrides. The silyl hydride can be a polysilane, a polysiloxane or a combination of polysilane and polysiloxanes.

Desirably, the silyl hydride is a polysiloxane molecule with one or more than one Si—H bond. If the silyl hydride is a polysiloxane, the Si—H bond is on the silicon atom of an M-type or D-type siloxane unit. The polysiloxane can be linear and comprise only M type and D type units. Alternatively, the polysiloxane can be branched and contain T type and/or Q type units.

Examples of suitable silyl hydrides include pentamethyldisiloxane, bis(trimethylsiloxy)methyl-silane, tetramethyldisiloxane, tetramethycyclotetrasiloxane, and hydride terminated poly(dimethylsiloxane) such as those available from Gelest under the tradenames: DMS-H03, DMS-H25, DMS-H31, and DMS-H41.

The concentration of silyl hydride is typically sufficient to provide a molar ratio of Si—H groups to siloxane linkages that is 0.2 or more, 0.5 or more, 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more 1.2 or more, 1.4 or more, 1.6 or more, 1.8 or more, 2.0 or more, 2.2 or more, even 2.5 or more while at the same time is typically 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, 2.8 or less, 2.5 or less, 2.3 or less, 2.0 or less, 1.8 or less, 1.6 or less, 1.4 or less, 1.2 or less or even 1.0 or less.

Either the siloxane or the silyl hydride (or both) can serve as crosslinkers in the reaction. A crosslinker has at least two reactive groups per molecule and reacts with two different molecules through those reactive groups to cross link those molecules together. Increasing the linear length between reactive groups in a crosslinker tends to increase the flexibility in the resulting crosslinked product. In contrast, shortening the linear length between reactive groups in a crosslinker tends to reduce the flexibility of a resulting crosslinked product. Generally, to achieve a more flexible crosslinked product a linear crosslinker is desired and the length between reactive sites is selected to achieve desired flexibility. To achieve a less flexible crosslinked product, shorter linear crosslinkers or even branched crosslinkers are desirable to reduce flexibility between crosslinked molecules.

The silyl hydride can be the same molecule as the siloxane—that is, a single molecule containing both a siloxane linkage and silyl hydride functionality can serve the roll as both the silyl hydride and siloxane. Alternatively, the silyl hydride can be a different molecule from the siloxane. The silyl hydride can be free of siloxane linkages. The siloxane can be free of silyl hydride groups.

The composition (and reaction process) of the present invention can comprise more than one silyl hydride, more than one siloxane and/or more than one component that serves as both a silyl hydride and siloxane.

Typically, the concentration of silyl hydride in the composition is 5 wt % or more, 10 wt % or more, 15 wt % or more, 20 wt % or more, even 25 wt % or more while at the same time is typically 30 wt % or less, 25 wt % or less, 20 wt % or less, 15 wt % or less or even 5 wt % or less based on combined weight of silyl hydride, siloxane, amine and Lewis acid catalyst in the composition.

Lewis Acid Catalyst

The Lewis acid catalyst is desirably selected from a group consisting of aluminum alkyls, aluminum aryls, aryl boranes, aryl boranes including triaryl borane (including substituted aryl and triaryl boranes such a tris(pentafluorophenyl)borane), boron halides, aluminum halides, gallium alkyls, gallium aryls, gallium halides, silylium cations and phosphonium cations. Examples of suitable aluminum alkyls include trimethylaluminum and triethylaluminum. Examples of suitable aluminum aryls include triphenyl aluminum and tris-pentafluorophenyl aluminum. Examples of triaryl boranes include those having the following formula:

where R is independently in each occurrence selected from H, F, Cl and CF₃. Examples of suitable boron halides include (CH₃CH₂)₂BCl and boron trifluoride. Examples of suitable aluminum halides include aluminum trichloride. Examples of suitable gallium alkyls include trimethyl gallium. Examples of suitable gallium aryls include tetraphenyl gallium. Examples of suitable gallium halides include trichlorogallium. Examples of suitable silylium cations include (CH₃CH₂)₃Si⁺X⁻ and Ph₃Si⁺X⁻. Examples of suitable phosphonium cations include F—P(C₆F₅)₃ ⁺X⁻.

The Lewis acid is typically present in the composition at a concentration of 10 weight parts per million (ppm) or more, 50 ppm or more, 150 ppm or more, 200 ppm or more, 250 ppm or more, 300 ppm or more, 350 ppm or more 400 ppm or more, 450 ppm or more, 500 ppm or more, 550 ppm or more, 600 ppm or more, 70 ppm or more 750 ppm or more, 1000 ppm or more 1500 ppm or more, 2000 ppm or more, 4000 ppm or more, 5000 ppm or more, even 7500 ppm or more, while at the same time is typically 10,000 or less, 7500 ppm or les, 5000 ppm or less, 1500 μm or less, 1000 ppm or less, or 750 ppm or less relative to combined weight of siloxane and silyl hydride in the composition.

Amine

The selection of amine is important because it must complex with the Lewis acid at 23° C. to inhibit catalytic activity of the Lewis acid in a reaction composition at that temperature, yet must release the Lewis acid at an elevated temperature so as to rapidly (within 10 minutes or less, preferably 5 minutes or less, more preferably one minute less) gel the reaction composition at 90° C. Reaction compositions can be monitored at 23° C. and 90° C. to determine gel times (see Example section below). Alternatively, or additionally, one can characterize by differential scanning calorimetry the temperature at which the curing reaction exotherm occurs (Tpeak, see Example section below for procedure). The Tpeak value for a composition should increase relative to the Tpeak for an identical amine-free composition if the proper amine is present, but desirably remains below 130° C., preferably below 120° C., more preferably below 110° C. so as to reflect dissociation sufficient to rapidly cure at 90° C.

Amines have been reported as irreversibly complexing with Lewis acid catalysts, except for triaryl amines which are reported to not compromise Lewis acid catalysts. Without being bound by theory, it seems the present invention is partly the result of discovering that by having one or more conjugated moeity attached the nitrogen of an amine through a conjugated carbon, the conjugated moiety helps delocalize the free electrons of the amine and weaken it as a Lewis base. As a result, amines having at least one conjugated moiety attached to the nitrogen of the amine through a conjugated carbon have been discovered to complex with and block Lewis acid catalyst at 23° C. so as preclude gelling of a reaction composition at 23° C. in 4 hours or less, preferably 8 hours or less, more preferably 10 hours or less, yet more preferably 12 hours less, while at the same time complexes weakly enough so as to release the Lewis acid catalyst upon heating to 90° C. so as to gel the composition in 10 minutes or less, preferably 5 minutes or less, more preferably one minute or less.

To be a sufficiently weak Lewis base, the amines of the present invention have at least one, preferably at least two, and can have three conjugated moieties attached to the nitrogen of the amine through a conjugated carbon so that the free electron pair on the nitrogen can dissociate with the conjugated moiety and weaken the amine as a Lewis base. Preferably, the conjugated moieties are aromatic moieties.

Triaryl amines have three aromatic conjugated moieties attached to the amine nitrogen each through a conjugated carbon. As a result, triaryl amines are examples of amines that optimally delocalize the nitrogen free electrons to create a weak Lewis base. That is consistent with prior art reporting that triaryl amines do not compromise Lewis acid catalysts. Nonetheless, triaryl amines have been surprisingly discovered to have a blocking effect on Lewis acid catalysts at 23° C. and inhibit Lewis acid catalyzed reaction at 23° C. and are in scope of the broadest scope of the amines suitable for use in the present invention. Desirably, the amines of the present invention are stronger Lewis bases than triaryl amines in order to achieve greater blocking effect (hence, longer shelf stability) at 23° C. In that regard, while the amine of the present invention can have one, two or three conjugated moieties attached to the nitrogen of the amine through a conjugated carbon, it is desirable that the amine is other than a triaryl amine. Compositions of the present invention can be free of triarylamines.

The ability of a conjugated moiety to weaken the strength of the amine as a Lewis base is further tunable with substituent groups that can be attached to the conjugated moiety. Including electron withdrawing groups (such as halogens) on the conjugated moiety will further draw the nitrogen electrons into the delocalized conjugated system and weaken the strength of the amine as a Lewis base. Including electron donating groups on the conjugated moiety has the opposite effect and increases the resulting amine strength as a Lewis base relative to the same amine with the conjugated moiety without the electron donating group(s).

The amine needs to be strong enough to bind to and block the Lewis acid catalyst at 23° C. in order to achieve shelf stability. The amine will release the acid at lower temperatures if it is a weaker Lewis base than if it were a stronger Lewis base. Hence, selection of the moieties attached to the nitrogen of the amine can be selected to achieve shelf stability and reactivity at a desired temperature.

It has further been discovered that suitable amines must have the amine nitrogen that is not a member of an N═C—N linkage such as in amidines, guanidines, and N-methylimidazole. Desirably, the composition is free of amines having an N═C—N linkage. For example, the composition can be free of amidines and guanidines.

In general, the amine has the following formula: R¹R²R³N; wherein each of R¹, R², and R³ is independently selected from a group consisting of hydrogen, alkyl, substituted alkyl, and conjugated moieties; and wherein at least one of R¹, R² and R³ is a conjugated moiety connected to the nitrogen by a conjugated carbon. One, two or three of R¹, R² and R³ can be a conjugated moiety connected to the nitrogen by a conjugated carbon. Desirably, the conjugated moiety is an aromatic moiety.

Examples of suitable amines for use in the present invention include any one or any combination of more than one amine selected from a group consisting of: aniline, 4-methylaniline, 4-fluoroaniline, 2-chloro-4-fluoroaniline, diphenylamine, diphenylmethylamine, triphenylamine, 1-naphthylamine, 2-naphthylamine, 1-aminoanthracene, 2-aminoanthracene, 9-aminoanthracene, β-aminostyrene, 1,3,5-hexatrien-1-amine, N,N-dimethyl-1,3,5-hexatrien-1-amine, 3-amino-2-propenal and 4-amino-3-buten-2-one.

The concentration of amine in the composition is at least at a molar equivalent to the concentration of Lewis acid catalyst so as to be able to complex with and block all of the Lewis acid catalyst at 23° C. The concentration of amine can exceed the molar concentration of Lewis acid catalyst, but preferably is present at a concentration of 110 mole-percent (mol %) or less, prefer 105 mol % or less, more preferably 103 mol % or less and most preferably 101 mol % or less while also being present at 100 mol % or more relative to total moles of Lewis acid catalyst.

The amine and Lewis acid form a complex in the composition that blocks the Lewis acid from catalyzing a reaction between the other composition components sufficiently to be shelf stable at 23° C. Upon heating, the amine releases the Lewis acid to allow the Lewis acid to catalyze a reaction.

Optional Components

Compositions of the present invention can consist of the silyl hydride, the alpha-beta unsaturated ester, the Lewis acid catalyst and the amine. Alternatively, the compositions of the present invention can further comprise one or a combination of more than one optional component. Optional components are desirably present at a concentration of 50 wt % or less, 40 wt % or less, 30 wt % or less, 20 wt % or less, 10 wt % or less, 5 wt % or less, or even one wt % or less based on composition weight.

Examples of possible optional components include one or a combination of more than one component selected from a group consisting of hydrocarbyl solvents (typically at a concentration of 10 wt % or less, 5 wt % or less, even one wt % or less based on composition weight), pigments such as carbon black or titanium dioxide, fillers such as metal oxides including SiO₂ (typically at a concentration of 50 wt % or less based on composition weight), moisture scavengers, fluorescent brighteners, stabilizers (such as antioxidants and ultraviolet stabilizers), and corrosion inhibitors. The compositions of the present invention also can be free of any one or any combination of more than one such additional components.

Notably, the composition of the present invention can contain one wt % or less, 0.5 wt % or less water relative to composition weight. Desirably, the composition is free of water.

Reaction Process

The present invention includes a chemical reaction process comprising the steps of: (a) providing a composition of the present invention; and (b) heating the composition to a temperature sufficient to dissociate the Lewis acid catalyst from the amine.

Step (a) can comprise mixing together an amine, Lewis acid catalyst, a silyl hydride and a siloxane. However, the Lewis acid catalyst and amine are combined so that the amine can complex with and block the catalytic activity of the Lewis acid prior to combining them with both of silyl hydride and siloxane. It is possible to prepare the Lewis acid/amine complex in the presence of one of the reactants (that is, the silyl hydride or the siloxane) provided the Lewis acid does not catalyze reaction with the one reactant. The amine and Lewis acid can be combined in a solvent, such as toluene, to form the blocked Lewis acid complex and then that complex can be combined with the silyl hydride and siloxane.

Step (b) generally requires heating the composition to a temperature of 80° C. or higher, preferably 90° C. or higher while at the same time generally can be accomplished by heating to a temperature of 300° C. or lower, 250° C. or lower, 200° C. or lower, 150° C. or lower, and can be 100° C. or lower.

The compositions of the present invention are particular useful as coatings. The compositions can also be useful form forming molded articles. In such an applications the process of the present invention can further comprise applying the composition to a substrate after step (a) and before or during step (b).

Examples

MD^(H) ₆₅M Silyl Hydride/Siloxane. Fit a 3-necked flask with a mechanical stirrer and add 40 grams (g) deionized water, 10 g heptane and 0.05 g tosylic acid. Add to this dropwise while stirring a mixture of 200 g methyldichlorosilane and 10 g trimethylchlorosilane over 30 minutes. Stir for an additional 60 minutes at 23° C. Wash the reaction solution three times with 50 milliliters (mL) deionized water each time. Dry the solution with anhydrous sodium sulfate and filter through activated carbon. Remove volatiles by Rotovap to obtain MD^(H) ₆₅M Silyl Hydride/Siloxane. These materials serve as both the silyl hydride and the siloxane components of the compositions.

M^(H)D₃₇₆M^(H) Silyl Hydride/Siloxane. This is commercially available as DMS-H31 from Gelest.

Catalyst Solution.

Prepare a catalyst solution by combining 5 wt % BCF in toluene with 5 wt % of specified amine (see Tables 1 and 2) in toluene at amounts sufficient to provide equi-molar amounts of BCF and amine (1:1 molar ratio) and approximately 12 grams of final solution. Sonicate the final solution for 30 seconds and let sit for 12 hours at 23° C. Add 0.5-1.0 gram of tetrahydrofuran to the final solution to help dissolve the BCF-amine complex and form the catalyst solution for use in the example compositions.

23° C. Stability Test. Prepare the composition in a vial and then seal the vial and store at 23° C. Check the flowability of the contents of the vial at by inverting the vials and watching the contents to determine if it flows. Check flowability on hour intervals for 8 hours and after than on 24 hour intervals. Record the time at which gelation occurs as evidenced by a failure of the vial contents to flow in 1-2 seconds upon inverting. The time at which gelation occurs is the “23° C. Shelf Life”. During the test, the composition are open to ambient (including ultraviolet) light.

Cure Speed at 90° C. The Cure Speed at 90° C. is the time it takes to form a gel or cured film free of a tacky surface at 90° C. Coat a 125 micrometer film of a composition on glassine paper substrate. Place the film in an oven at 90° C. Check the films for tackiness every 30 seconds. The time required to achieve a tack-free film is the Cure Speed at 90° C. Tpeak. Tpeak is the temperature where there is maximum reaction exotherm in a reaction system. Determine Tpeak by differential scanning calorimetry (DSC) for a sample composition. Characterize by DSC by loading a 10 milligram sample of a composition into a DSC pan and conducting DSC using a temperature ramp from 10° C. to 250° C. at a rate of 10° C. per minute. Tpeak is the temperature at which maximum exotherm is evident in the DSC curve.

Comparative Examples (Comp Exs) A-D: Effect of Different Lewis Acid Catalysts

Comp Exs A-D illustrate the efficacy of BCF as a catalyst for the rearrangement reaction between a silyl hydride and siloxane. The Comp Exs A-D demonstrate the 23° C. Shelf Life of a composition with two different Lewis acid catalysts without inhibitor present and reveal that BCF is more effective than either super base catalyst 1,8-Diazabicyclo[5.4.0]undec-7-ene (“DBU”), or platinum (“Pt” in the form of Karstedt's catalyst) at catalyzing the reaction of silyl hydride and siloxane. At lower loading levels, BCF cures MD^(H) ₆₅M an order of magnitude faster than DBU and at equal loading with the Pt catalyst cures MD^(H) ₆₅M almost two orders of magnitude faster at 23° C. In view of these results, further experiments use BCF, because it is proven to be a highly effective Lewis acid catalyst for this reaction.

Comp Ex A (DBU, 1000 ppm). Add by micropipette a solution of 1000 ppm DBU dissolved in a minimum amount of toluene to 2 grams (g) MD^(H) ₆₅M in a 10 g dental cup. Quickly shake the cup and leave it at 23° C. and monitor curing by touching with a polypropylene pipette and record when the mixture becomes fully gelled. It took approximately 50 minutes to gel at 23° C.

Comp Ex B (Pt, 100 ppm). Add by micropipette a solution of 100 ppm Karstedt's catalyst (organoplatinum compound derived from divinyl-containing disiloxane, available from Sigma-Aldrich) dissolved in a minimum amount of toluene to 2 grams (g) MD^(H) ₆₅M in a 10 g dental cup. Quickly shake the cup and leave it at 23° C. and monitor curing by touching with a polypropylene pipette and record when the mixture becomes fully gelled. It took approximately 2 hours to gel.

Comp Ex C (BCF 500 ppm). Add by micropipette a solution of 500 ppm BCF dissolved in a minimum amount of toluene to 2 grams (g) MD^(H) ₆₅M in a 10 g dental cup. Quickly shake the cup and leave it at 23° C. and monitor curing by touching with a polypropylene pipette and record when the mixture becomes fully gelled. It took approximately 4 minutes to gel.

Comp Ex D (BCF, 100 ppm). Add by micropipette a solution of 100 ppm BCF dissolved in a minimum amount of toluene to 2 grams (g) MD^(H) ₆₅M in a 10 g dental cup. Quickly shake the cup and leave it at 23° C. and monitor curing by touching with a polypropylene pipette and record when the mixture becomes fully gelled. It took approximately 6 minutes to gel.

Comparative Examples E-G: Effect of Amine Lacking Conjugated Carbon Bond to Amine Nitrogen as Blocking Agents

Comp Exs E-G use a 500 ppm loading of BCF (like Comp Ex C) except the BCF is complexed with an amine blocking agent that does not have a conjugated carbon attached to the amine nitrogen. The compositions are characterized for the effect of the blocking agent on 23° C. Shelf Life and 90° C. Cure Speed. Comp Exs E-G demonstrate long 23° C. Shelf Life, but unacceptably long (greater than 2 hour) 90° C. Cure Speed. These results are consistent with prior art conclusions that amines essentially irreversibly complex with Lewis acids to inhibit the Lewis acid efficacy as a reaction catalyst.

Comp Ex E-G Procedure. Add by micropipette sufficient catalyst solution containing BCF complexed with an amine inhibitor so as to introduce 500 ppm BCF to 2 grams (g) MD^(H) ₆₅M in a 10 g dental cup. Quickly shake the cup and leave it at 23° C. and monitor curing by touching with a polypropylene pipette and record when the mixture becomes fully gelled. Determine 90° C. Cure Speed of the sample as described for that test method above. Table 1 identifies the amine inhibitor, 23° C. Shelf Life and 90° C. Cure Speed for these samples.

TABLE 1 23° C. 90° C. Sample Inhibitor Shelf Life Cure Speed Comp Ex E butyl amine >48 hours >2 hours Comp Ex F diisopropyl amine >48 hours >2 hours Comp Ex G N-methylimidazole >48 hours >2 hours

Comparative Example H and Examples (Exs) 1-4: Effect of Amine with Conjugated Carbon Bond to Amine Nitrogen as Blocking Agents

Comp Ex H serves as a reference without an inhibitor (blocking agent) on the BCF Lewis acid catalyst in a reaction with two different reactants present. Exs 1˜4 demonstrate the efficacy of an amine blocking agent having a conjugated carbon attached to the amine nitrogen as blocking the Lewis acid catalyst at 23° C. yet freeing the Lewis acid catalyst at 90° C. Comp Ex H and Exs 1-3 all use 500 ppm BCF. Ex 4 uses 300 ppm BCF. Ex 1 uses the MD^(H) ₆₅M reactant of the previous Comp Exs. Comp Ex H and Exs 2-4 use a reactant blend of 30 wt % MD^(H) ₆₅M and 70 wt % M^(H)D₃₇₆M^(H) with wt % relative to reactant weight. The Samples were clear and free of bubbles once gelled or cured.

Ex 1. Add by micropipette sufficient catalyst solution containing BCF complexed with an aniline so as to introduce 500 ppm BCF to 2 grams (g) MD^(H) ₆₅M in a 10 g dental cup. Quickly shake the cup and leave it at 23° C. and monitor curing by touching with a polypropylene pipette and record when the mixture becomes fully gelled. Determine 90° C. Cure Speed of the sample as described for that test method above. Table 2 identifies the amine inhibitor, 23° C. Shelf Life and 90° C. Cure Speed for these samples.

Comp Ex H. Add by micropipette sufficient catalyst solution containing 500 ppm BCF dissolved in a minimal amount of toluene to a mixture of 1.4 g M^(H)D₃₇₆M^(H) and 0.6 g MD^(H) ₆₅M in a 10 g dental cup. Quickly shake the cup and leave it at 23° C. and monitor curing by touching with a polypropylene pipette and record when the mixture becomes fully gelled. Determine 90° C. Cure Speed of the sample as described for that test method above. Table 2 identifies the amine inhibitor, 23° C. Shelf Life and 90° C. Cure Speed for these samples.

Exs 2-3. Add by micropipette sufficient catalyst solution containing BCF complexed with the inhibitor identified in Table 2 so as to introduce 500 ppm BCF to a mixture of 1.4 g M^(H)D₃₇₆M^(H) and 0.6 g MD^(H) ₆₅M in a 10 g dental cup. Quickly shake the cup and leave it at 23° C. and monitor curing by touching with a polypropylene pipette and record when the mixture becomes fully gelled. Determine 90° C. Cure Speed of the sample as described for that test method above. Table 2 identifies the amine inhibitor, 23° C. Shelf Life and 90° C. Cure Speed for these samples.

Ex 4. Add by micropipette sufficient catalyst solution containing BCF complexed with the aniline so as to introduce 300 ppm BCF to a mixture of 1.4 g M^(H)D₃₇₆M^(H) and 0.6 g MD^(H) ₆₅M in a 10 g dental cup. Quickly shake the cup and leave it at 23° C. and monitor curing by touching with a polypropylene pipette and record when the mixture becomes fully gelled. Determine 90° C. Cure Speed of the sample as described for that test method above. Table 2 identifies the amine inhibitor, 23° C. Shelf Life and 90° C. Cure Speed for these samples.

TABLE 2 23° C. 90° C. Sample Inhibitor Lewis Acid Shelf Life Cure Speed Ex 1 Aniline 500 ppm BCF  6 hours 2 minutes Comp (none) 500 ppm BCF  8 minutes NM* Ex H Ex 2 p-anisidine 500 ppm BCF 30 hours 6 minutes Ex 3 aniline 500 ppm BCF  8 hours 3 minutes Ex 4 aniline 300 ppm BCF >5 hours 5 minutes** *If sample gelled in less than 10 minutes at 23° C. cure speed at 90° C. was not measured. **This sample was cured in an aluminum dish at 90° C. rather than think film so it is longer than expected for thin film cure speed.

The Examples reveal that amines having a conjugated carbon attached to the amine nitrogen block the Lewis acid catalyst to provide compositions that are stable at 23° C., but release the Lewis acid when heated to provide rapid (<10 minutes) curing at 90° C. 

1. A composition comprising a mixture of silyl hydride, a siloxane, a Lewis acid catalyst comprising an aryl borane, and an amine having the following formula: R¹R²R³N; where the nitrogen is not a member of an N═C—N linkage and where each of R¹, R², and R³ is independently selected from a group consisting of hydrogen, alkyl, substituted alkyl, and conjugated moieties; and wherein at least one of R¹, R² and R³ is a conjugated moiety connected to the nitrogen by a conjugated carbon, wherein the siloxane in the composition has a concentration of 70 weight % or more, and the silyl hydride in the composition has a concentration of 5 weight % or more each based on combined weight of silyl hydride, siloxane, amine, and Lewis acid catalyst.
 2. The composition of claim 1, wherein the conjugated moiety is an aromatic moiety.
 3. The composition of claim 1, wherein at least two of R¹, R², and R³ are conjugated moieties connected to N by a conjugated carbon.
 4. The composition of claim 1, wherein the Lewis acid catalyst is an aryl borane of formula

where R is independently in each occurrence selected from H, F, Cl and CF₃.
 5. The composition of claim 4, wherein the Lewis acid catalyst is a fluorinated aryl borane.
 6. The composition of claim 1, wherein the silyl hydride and the siloxane are the same molecule.
 7. The composition of claim 1, wherein the composition is free of a UV light sensitive blocking agent for the Lewis acid catalyst.
 8. A process comprising the steps of: (a) providing a composition of claim 1; and (b) heating the composition to a temperature sufficient to dissociate the Lewis acid catalyst from the amine.
 9. The process of claim 8, wherein step (a) comprises mixing together an amine, Lewis acid catalyst, a silyl hydride and a siloxane provided the Lewis acid catalyst and amine are combined so that the amine can complex with and block the catalytic activity of the Lewis acid prior to combining them with both of silyl hydride and siloxane.
 10. The process of claim 8, wherein the process further includes a step of applying the composition to a substrate or placing the composition in a mold after step (a) and before or during step (b). 